Wiring the Brain

So many things can go wrong in the development of the human brain it is amazing that it ever goes right.   The fact that it usually does – that the majority of people do not suffer from a neurodevelopmental disorder – is due to the property engineers call robustness .   This property has important implications for understanding the genetic architecture of neurodevelopmental disorders – what kinds of insults will the system be able to tolerate and what kind will it be vulnerable to? The development of the brain involves many thousands of different gene products acting in hundreds of distinct molecular and cellular processes, all tightly coordinated in space and time – from patterning and proliferation to cell migration, axon guidance, synapse formation and many others.   Large numbers of proteins are involved in the biochemical pathways and networks underlying each cell biological process.   Each of these systems has evolved not just to do a particular job, but

A trio of papers in this week’s Nature identifies mutations causing autism in four new genes, demonstrate the importance of de novo mutations in the etiology of this disorder and suggest that there may be 1,000 or more genes in which high-risk, autism-causing mutations can occur. These studies provide an explanation for what seems like a paradox: on the one hand, twin studies show that autism is very strongly genetic (identical twins are much more likely to share a diagnosis than fraternal twins) – on the other, many cases are sporadic, with no one else in the family affected. How can the condition be “genetic” but not always run in the family? The explanation is that many cases are caused by new mutations – ones that arise in the germline of the parents. (This is similar to conditions like Down syndrome). The studies reported in Nature are trying to find those mutations and see which genes are affected. They are only possible because of the tremendous advances in our ability to